Hepatic gluconeogenesis is one of the critical factors in the development of hyperglycemia in diabetes. The sustained"pfo'ductiorTof"glucose by the liverrequireTtuffiaenrmetabollc substrates saerras~pyravate, lactate, and alanine. Among them, pyruvate is the most direct substrate used for hepatic gluconeogenesis. Since substrate availability is one of the most important driving forces in gluconeogenesis, regulation of pyruvate metabolism may be a critical switch for glucose oxidation or gluconeogenesis. Pyruvate dehydrogenase kinases (PDK) normally inhibits pyruvate oxidation through phosphorylation and inactivation of the pyruvate dehydrogenase complex. One of the PDK kinases, PDK4, is elevated in the liver under starvation or diabetic conditions, suggesting that regulation of PDK4 may be an essential component of gluconeogenesis because of its effects on substrate availability. To elucidate the mechanisms of glucose homeostasis and PDK4 gene regulation under normal and diabetic conditions, the following specific aims are proposed. Aim 1, The role of PDKs in gluconeogenesis in the development of diabetes will be examined using animal models. Aim 2, Regulation of PDK4 gene expression by nutrient signals will be investigated by both in vitro and in vivo approaches. Aim 3, Role of Foxol in the regulation of PDK4 and hepatic glucose homeostasis will be investigated using mouse genetic approaches.